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					                                             APEX 2A Facility

    APEX Heterodyne Facility                                       APEX 1 Channel Optics           APEX 2a Channel Optics

     Receiver Development
Onsala Space Observatory, Sweden, via its Group for
Advanced Receiver Development has responsibility for
APEX Project heterodyne facility receivers installed in
the Nasmyth Cabin A. The facility receivers should
cover the following frequencies:
Table 1
          Band      RF range (GHz) IF (GHz)
  APEX-1 (2SB)            211-275            4-8
  APEX-2 (2SB)            275-370            4-8
  APEX-3 (2SB)            385-500            4-8
  APEX-T2 (BLs)           1320±70            2-4
In order to facilitate availability of the APEX facility
heterodyne instruments we proceed our work in two
steps, when the First Light Receiver comprises the two
receiver channels, APEX 2a with DSB technology
(installed at the telescope in March-April 2005) and
APEX 1a (2SB) to be placed in the dewar during the fall

   First-Light Facility Receiver                           Figure 1. Inside APEX First Light Receiver: optics,
                                                           cryogenics and APEX B1 and B2 channel components.
The cryostat is a hybrid closed-system using a Gifford
Mac-Mahon 2-stage refrigerator, together with a Joule-                            400mm
Thomson the third stagerefrigerator. The 2-stage gives
a temperatures of about 80 K and 15 K for the outer
shields. The Joule-Thomson circuitry cools the helium
gas further where it condensates with a slight
overpressure of 0.2 bar (giving about 4.5 K at sea level
and 4.0 K at 5000 m). The cooling takes usually about
12-15 hours. The mixer block is connected directly to
the IF 4-8 GHz isolator and to the IF amplifier, to                             Nasmyth flange
minimize losses. A 2nd cold amplifier is on the 15 K

cooling stage.
                                                                                Switching active
The receiver optics consists of cold mirrors, one flat                               mirror

and one active, which are combined with another active
mirror outside the cryostat. The position and focusing
properties of the mirrors and the used corrugated feed
horn of the mixer have been chosen such that, with                         ellipsoid mirror

another pair of active mirrors in the Cassegrain cabin,                           Horn aperture
optics produces a frequency independent illumination                                position
for the telescope secondary for the frequency range for
each receiver channel in the band of approximately
210-1500 GHz.
                                                           Figure 2. Optics for the APEX B2A receiver channel, the
                                                           picture of the First Light Receiver installed at APEX.
                 6-channel Facility Receiver Development
The 6 – channel Facility Receiver with the entire suite      The two most challenging receiver channels within
of the receiver channels as in the Table above should        responsibility of Onsala / GARD for APEX 6-channel
be available on the second half of 2006. The two             receiver are APEX Band 3 and APEX T2.
additional channels, compared to the listed in the           We are developing sideband separation technology for
Table 1 are APEX 4 (DSB?) 602-700 GHz and APEX 5             the APEX Band 3 385-500 GHz to maximize possible
(DSB?) 787-950 GHz. The major challenge in the               scientific usefulness of this instrument.
designing this 6-chanell receiver is its complexity due to
operation at cryogenic temperature 4K, many channels,
optical layout and extremely wide frequency range 211-
1500 GHz. In order to achieve the required performance
a complex set of mirrors should be used together with
perfect cryogenic design and switching mirrors selecting
particular channel.

                                                             Figure 4. APEX 3 mixer chip layout and its matching
                                                             Another exciting development is APEX Band T2
                                                             1320±70 GHz. In order to be able to cover this
                                                             extremely high frequencies we will use balanced
                                                             waveguide mixer with the rectangular waveguide
                                                             dimensions as small as 90 x 180 μm.

                                                                                                  10 μm

                                                                              1 mm

Figure 3. Optical and cryogenic design of 6-channel          Figure 5. Scanning Electron Microscope picture of the
Facility Receiver.                                           APEX T2 balanced waveguide mixer block.